This invention relates in general to the manufacture of slip joints, such as are commonly used in vehicle drive train systems, for transmitting rotational force or torque between axially movable components. In particular, this invention relates to a method and apparatus for re-shaping portions of a low friction coating applied to the splines of one of such components in order to minimize broken back between the intermeshing splines of the axially movable components.
In most land vehicles in use today, a drive train system is provided for transmitting rotational power from an engine/transmission assembly to an axle assembly so as to rotatably drive one or more wheels of the vehicle. To accomplish this, a driveshaft assembly is usually connected between an output shaft of the engine/transmission assembly and an input shaft of the axle assembly. Typically, a first universal joint is connected between the output shaft of the engine/transmission assembly and a first end of the driveshaft assembly, while a second universal joint is connected between a second end of the driveshaft assembly and the input shaft of the axle assembly. The universal joints provide a rotational driving connection from the output shaft of the engine/transmission assembly through the driveshaft assembly to the input shaft of the axle assembly, while accommodating a limited amount of angular misalignment between the rotational axes thereof.
Not only must the drive train system accommodate a limited amount of angular misalignment between the engine/transmission assembly and the axle assembly, but it must also typically accommodate a limited amount of relative axial movement. A small amount of such relative axial movement frequently occurs when the vehicle is operated. To address this, it is known to provide one or more slip joints in the driveshaft assembly of the drive train system. A typical slip joint includes first and second splined members that are connected to respective components of the drive train system between the output shaft of the engine/transmission assembly and the input shaft of the axle assembly. The splined members cooperate with one another to provide a rotational driving connection between such components of the drive train system, while permitting a limited amount of relative axial movement therebetween.
As is well known in the art, one or both of the splined members may be coated with a material having a relatively low coefficient of friction. The low friction coating is provided to minimize the amount of force required to effect relative movement between the two splined members. Also, the low friction coating provides a relatively tight fit between the cooperating splines of the two splined members, thus minimizing any undesirable looseness therebetween while continuing to allow free axial movement.
A number of methods are known for applying the low friction coating to the splined members of the slip joint In one known method, the splined region of the slip joint member is first primed, then dipped into a molten bath of the low friction coating. In another known method, the splined region of the slip joint member is initially heated, then immersed in a bed containing a quantity of the low friction coating in particulate form. Alternatively, the splines can be coated electrostatically, wherein the low friction coating is applied in a particulate form. It is also known to apply the low friction coating by injection molding the low friction material between the assembled splined members.
One problem that has been experienced in connection with slip joints manufactured according to known methods is that even after the coating has been applied, an undesirable gap can still exist between adjacent splines formed on the cooperating members of the slip joint. These gaps can occur as a result of manufacturing tolerances in the formation of the individual splined members and the coating process and usually result in an undesirable amount of looseness between the splined members during operation. Looseness that occurs in the direction of rotation of the splined members, wherein one of the splined members can rotate slightly relative to the other splined member, is referred to as backlash. Looseness that occurs in the direction transverse to the direction of rotation of the slip joint, wherein one of the splined members can extend slightly at a cantilevered angle relative to the other splined member, is referred to as broken back. Known solutions to the problems of backlash and broken back have been found to be relatively difficult, costly, and time consuming to employ. Thus, it would be desirable to provide a method and apparatus for quickly and easily re-shaping portions of a low friction coating that has been applied to the splines of a component of a slip joint or other component in order to minimize such undesirable looseness.
This invention relates to a method and apparatus for re-shaping portions of a low friction coating applied to the surface of a component, such as to the outer surface of a spline formed on a component in a slip joint. The tool includes a collet having a first end that is threaded and a second end that is slotted to define a plurality of flexible arms. A wheel is rotatably supported on each of the arms of the collet. Portions of the outer circumferential surfaces of the wheels extend radially inwardly from the inner surface of the collet and are formed having a shape, such as plurality of circumferential ridges, that corresponds to the desired final shape for the coating applied to the surface of the component. The tool also includes a sleeve that is sized to be disposed co-axially about the collet. Preferably, the inner surface of the sleeve is sized to be slightly larger than the threaded first end of the collet, but slightly smaller than the arms of the second end thereof. Lastly, the tool includes a nut having an inner threaded surface that is sized to be threaded onto the threaded first end of the collet. The tool is initially installed by disposing the collet co-axially about the component. Then, the sleeve of the tool is disposed co-axially about the collet. Next, the nut is threaded onto the threaded first end of the collet. As the nut is threaded onto the collet, it engages the end of the sleeve and moves the sleeve axially toward the arms of the collet, causing the arms to be compressed radially inwardly toward one another such that the outer circumferential surfaces of the wheels engage the coating provided on the outer surface of the component. As a result, the coating is re-shaped to have an undulating or sawtooth cross sectional shape that corresponds to the shape of the outer circumferential surfaces of the wheels. The tool as a whole can then be moved axially back and forth along the surface of the component to re-shape the entire length of the coating thereon.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.